rural residential waste water/effluent treatment

I am developing a 48 lot rural residential subdivision set in 700 
hectares of eucalypt timberland and improved and native pasture. The 
layout comprises  five clusters of 8-14  lots each set out along a 
connecting road.
We intend to require each residence to install a conventional septic tank 
to receive all waste water on a given lot , with the overflow of each 
septic tank on each lot connected to a 90mm upvc pipe leading to a common 
useage ponding system. The concept involves the construction of the first 
pond so that an average depth of waste water of 1.2m is maintained with 
retention of wate water in the first pond for a minimum 30 days 
overflowing into a second pond for retention for a further 120 days. The 
water then remaining may be used for spray irrigation in pasture.
The exposure of such waste water to sunlight should remove all bacteria.

Any persons having experience of such a system and knowledge of suitable 
design parameters please contact me. 
Robert Hood  rhood@ix.net.au